In the series It's all about struggling to find water. I guess I missed an explanation somewhere.

It's just bugging me that with those advanced techs and ice asteroids and earth's water and ice in the mars's poles, Why in such a future people are fighting over water?

  • Earth has enough water for any solar colonies, a donation of water could stop a war. Some less water is better than an interplanetary war right?
  • They got energy they can extract water from thin air by Gathering Oxygen and Hydrogen, at least enough to survive or at an extreme level break up or join atoms in nuclear reactions to get oxygen (high tech but it's future)
  • If those people are alive it means they have enough water to survive, why don't they recycle their current reserves of water, Like recycling urine, dead bodies, ... ? Even water evaporates can be taken from air since they are living in an isolated space.
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    Just to reinforce a point made in my answer, Earth doesn't even have enough water for the Earth, much less solar colonies. There is a theory (I believe formulated by historians) that many or all of wars are, in the end, fought over water. There's another theory that as the population grows and potable water supplies shrink, water wars are going to become a lot more common. Those theories might not hold water (ha ha), but water scarcity is a real thing on Earth. It certainly wouldn't be any better in space. May 22, 2018 at 15:09
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    Here's a pretty good coverage of the issue on the SciFi stack, where the main answers were drawn more from the source novels - scifi.stackexchange.com/questions/111942/… May 22, 2018 at 15:23
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    Water is scarce in the solar system (in reality), that is why it was such a big deal to find some on mars.
    – Polygnome
    May 22, 2018 at 17:31
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    @ToddWilcox - note that FRESH water is scare, more so than water. We have lots of water. If desalination plants were cheap, plentiful, and sustainable, there would not be globalised water scarcity. There may still be water scarcity is certain locations, far from the ocean).
    – Scott
    May 23, 2018 at 1:39
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    @Polygnome Water isn't scarce in the Solar System. Mars is estimated to have 5 million m^3 at the poles and that's just what's near the surface. Ceres is literally spewing water. Plumes have been detected putting out 3 kg of water per second. The surface of Ceres is water ice, carbonates, and clay. The mantle is estimated to contain 200 million km^3 of water, more than all the fresh water on Earth.
    – Schwern
    May 23, 2018 at 6:00

3 Answers 3


Right now there are many people struggling on Earth to get clean drinking water, so water scarcity is a real world thing that certainly wouldn't be any better for spacefarers.

One problem with water that is on the Earth is that it's very expensive to send it into space. That's analogous to the problem of moving water around on the Earth. Sure there's plenty of total water on the Earth right now, but most of it would require a lot of expensive processing to make it drinkable, and even then, it would take expensive transportation to get it to everyone who needs it.

Even if the cost of transporting the water were feasible, then there's the time. Without a large existing fleet of water tankers, it would be hard to get water to the whole solar system fast enough. Meaning, it could take years to get a reasonable amount of water to the moons of Jupiter.

Shipping water from Earth only delays the problem. The more water you ship, the more comfortable things get for spacefarers and they will live longer and have more children, which means you have to ship even more water and now you're just accelerating the pace of the depletion of the Earth's water, and permanently removing water from the Earth's water cycle. So shipping water from the Earth is a very bad idea.

One more note about shipping water from Earth: It's very likely that not everyone on Earth would agree that shipping water is better than interplanetary war. If I remember correctly, there are warmongering factions on Earth. In human history, many people have seen wars as opportunities to gain land or economic advantage. World War I wasn't exactly caused by the assassination of Archduke Ferdinand, it was more about several European countries wanting a war and the assassination gave them the pretext they needed.

Extracting water from "air" requires first that the air actually have both hydrogen and oxygen in it, and while we can assume that life support atmosphere has oxygen, it wouldn't make a lot of sense to go through the trouble to put hydrogen in it. Also, the oxygen in the life support atmosphere is there so the humans can breathe it, and oxygen is much more precious than water, in the short term. Finally, the process for turning gaseous hydrogen and oxygen into water is called "burning", and fires are generally bad in space. A controlled fire could be one way to get some water from gaseous hydrogen and oxygen, but that's hard to do and again you're using up valuable gaseous oxygen (and where's the hydrogen from? Fuel? Delta-v is pretty valuable in space, also).

They probably are recycling all the water they can, but as the population grows, the need for water grows, so there has to be some net influx of water. Also, some water is lost to space and other places. It could be bound up in manufactured products, for example.

Two interesting books that deal with the problems of water in space are The Moon Is A Harsh Mistress by Robert Heinlein, and The Martian by Andy Weir. The former discusses the challenges of shipping water between the moon and the Earth, while the latter actually features a process of converting fuel to gaseous hydrogen and then gaseous hydrogen and oxygen into water in a closed system.

As PoloHoleSet has commented, there's an in-universe explanation for this here: https://scifi.stackexchange.com/questions/111942/why-is-water-so-rare-in-the-expanse

To summarize Valorum's Sci Fi Stack answer:

  • Overpopulation/population growth, as alluded to in my comments above
  • Destruction of an expected water shipment has caused a short-term crisis
  • Political tension is inhibiting the water trade
  • Some water is being wasted

Basically, water issues in space in The Expanse mirror the real-world water issues that exist on the Earth today.

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    Additionally, shipping water from Earth is significantly uphill. Shipping it from the asteroid belt is, by comparison, downhill. ie no escape velocity.
    – Tetsujin
    May 22, 2018 at 15:53
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    @Tetsujin Exactly. That's what I was trying to summarize with the word "expensive". May 22, 2018 at 15:59
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    As you mentioned and alluded to - I would think that grabbing huge chunks of deeply frozen space-ice, closer to where it is needed, and not bound by a planetary gravity field would be logistically much more practical than trying to take initially liquid water from Earth, get it into some sort of ship-able container or state, then launch it out of our gravity to a remote location. May 22, 2018 at 20:35
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    @PoloHoleSet Which they are doing at the very beginning of The Expanse--the Canterbury (among others) hauls ice from Saturn to other places in the Belt. There's plenty there, but it's a long haul, and demand is high, so the price is high too.
    – Ian
    May 23, 2018 at 0:14
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    One very important bit - they're not using water just for drinking. It's their propellant as well (obviously). They need to haul stuff, and that's the part that cannot be recycled even in principle - it's lost to space. As for hydrogen, almost all of it is sourced from water or hydrated minerals in the first place (though on Earth, you need to go far back to notice - e.g. a lot of hydrogen is produced during oil mining, but that got there in the first place from the plants and algae that first processed it from water). Talking about rocky planet/oids, of course - gas giants are different.
    – Luaan
    May 23, 2018 at 6:47

Some information missing from the other two answers. The MCRN is in the process of terraforming Mars, and as part of that are taking up quite a bit of the available water in the system. This, among the other problems, puts a significant strain on the water supply in the system.

Also, even on Ceres, the water doesn't go there and stay there. Ships that dock require water for it's inhabitants to survive.

Also in Season 1, it's mentioned that the Nauvoo has been delayed in part because of the super tight restrictions on resource loss from its systems. One can extrapolate from that to mean that other ships and habitats operate at a loss, hence part of the reason for the need for resupply at places like Ceres.


AFAIK the correct answer isn't scarcity. There is PLENTY of water in space. The overriding concern is ∆v.

Space travel is energy intensive and requires expensive hardware, and is therefore costly. Water is dumb, heavy mass, and humans need a lot of it. Any mass dedicated to hauling water could be instead used to hall smarter matter, or propellant (if it isn't water).

  • By "mass" in the second paragraph are you talking about reaction mass? (propellant?) May 23, 2018 at 18:08
  • While the core of your answer is in fact correct; the answer suffers from quality issues. I don't think anyone who doesn't already know what you do understands what you mean by your answer. To clarify: the main issue is the effort required to move water from place to place. Water is really heavy to ship a large quantity of. Think of it like this: would you rather pack 10 bowling balls in your bag and carry them to the other side of the country, or would you rather just sell the balls and buy new ones in your destination, saving you the trouble of having to transport the heavy bowling balls?
    – Flater
    Dec 30, 2018 at 10:40
  • Back of the napkin example: Humans use 80-100 gallons of water a day. Let's say massive technological advances have pushed that down to 5 gallons, or roughly 20 liters a day. I know this number is based on things that spacefarers don't have to do (watering a garden, taking a bath, ...), but I'm also omitting agricultural water usage which is a massive swing in the other direction. 20 liters is 20kg per person per day. Even if you assume no water losses are incurred, you always need 20kg for every additional human when [..]
    – Flater
    Dec 30, 2018 at 10:47
  • [..] the population expands. The world's population has grown by 81,362,400 people in 2018. That means that in one year, you need to find 81,362,400 x 20 = 1.6 billion liters of water just to cover the growing population. The Roci is about as big as the space shuttle. The space shuttle cargo hold is 74.3 m³ at full capacity, that's 74,300 liters. [..]
    – Flater
    Dec 30, 2018 at 10:53
  • [..] That means you need about 21,900 runs a year to bring the needed 1.6bn lliters of water in. That's 60 runs/day. And that's assuming that you can easily get water and are only focusing on the issue of transporting it, not locating it to begin with. However, the weight limitation is more severe: the space shuttlme can only carry 22,700 kg of cargo, which is 22,700 liters. That's about 1/3 of the volume limit, and thus you would need 180 runs/day, with no delays or failures or losses, just to deliver the water.
    – Flater
    Dec 30, 2018 at 10:55

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